She looked at research conducted by people like Richard Wener, a professor of environmental psychology at New York University and a longtime commuter, to find out how our daily commutes are affecting our health.

Here are three of the most insidious ways your commute can hurt you in the long run:

1. Commuting may raise your cortisol levels

Levy reported that in a 2004 study of suburban rail commuters taking the train from New Jersey to Manhattan, "Wener and his coauthor Gary Evans found that the longer their test subjects' journey was, the higher the levels of cortisol (the primary stress hormone) in their saliva, and the more difficult they found to focus on the task of proofreading assigned them at the end of their commute."

Invasions of personal space — something many more commuters will have to deal with this summer — "had an affect on cortisol levels, too, Wener and Evans concluded in a follow-up paper," she says.

"Chronic stress and overexposure to cortisol — which increases sugars in your bloodstream, alters your immune system responses, suppresses your digestive and reproductive systems, and communicates with that part of your brain that controls mood, motivation and fear — puts you at risk for mental health problems like anxiety and depression, and a whole host of physical health issues," writes Levy.

2. People with long commutes tend to get less sleep and exercise, and have higher cholesterol and BMI

Levy cites a 2009 study based on data from the American Time Use survey, which found that each minute spent commuting translates into a 0.22 minute sleep time reduction. "If you commute an hour each way, you're losing 26.5 minutes of sleep each day and 2.2 hours a week," she says. And, as we know, a lack of sleep can lead to many different health problems.

Employees with lengthy commutes were also more likely to report a diagnosis of high cholesterol and a body mass index (BMI) that categorized them as obese, according to the 2010 Gallup-Healthways Well-Being Index.

"That's in part because the time we spend on the subway or the road is time we aren't using to exercise or prepare food at home," Levy writes.

3. Having to make transfers during your commutes may raise stress levels even more

The Journal News reports that Amtrak is shifting some trains to Grand Central in order to deal with track problems at Penn Station. And New Jersey Transit commuters are being redirected to Hoboken Terminal in New Jersey, where they'll have to transfer to ferries, buses, or PATH trains to get into New York City, the New York Times reports.

The process has seemingly gone relatively smoothly so far, but any solutions that involve adding more transfers can take a toll on individual travelers.

Wener and Evans' research also supported the theory that the more transfers a commuter has, and the more difficult they are, the more stressed he or she becomes, reported Levy. "That's because transfers add an element of unpredictability to our travels."

She added: "Waiting for subways and buses is particularly exasperating when we have no idea how long the delay will be."